Field of the Invention
The present invention relates to electromagnetic band-gap (EBG) structures that inhibit the propagation of electromagnetic waves in specific frequency bands.
Description of the Related Art
Electromagnetic band-gap techniques that inhibit the propagation of electromagnetic waves in specific frequency bands are currently being researched. Electromagnetic band-gap structures exhibit a magnetic wall effect, and thus are valuable when used to reduce the profile of an antenna. A mushroom structure, in which patch conductors are arranged in an array in the same plane at constant gap intervals and conduction vias are connected from the patch conductors to ground conductors that are parallel to the patch conductors (see Japanese Patent Laid-Open No. 2002-510886, for example), is generally used as an electromagnetic band-gap structure. Meanwhile, Japanese Patent Laid-Open No. 2010-010183 proposes an electromagnetic band-gap structure in which an open stub is inserted between two conductor plates arranged in parallel. Meanwhile, International Publication No. 2010/013496 discloses a electromagnetic band-gap structure configured using short stubs or open stubs on outer sides of two conductor plates arranged in parallel. An electromagnetic band-gap structure in which two open stubs having different lengths are laid in the same layer has also been proposed.
A conventional mushroom-type electromagnetic band-gap structure has a problem in that the size of a single cell is large, and thus the structure is not suited for use in small-sized electronic devices. Meanwhile, an electromagnetic band-gap structure using open stubs has a problem in that because the open stubs are longer than short stubs, an electromagnetic band-gap structure using open stubs has a larger cell size than an electromagnetic band-gap structure using short stubs. There is a further problem in that because the size of a single cell is large, the electromagnetic band-gap band (blocking band) cannot be designed with a high degree of freedom.